Process for concentrating rubber latex and similar vegetable juices



Patented June 7, '1938 I I I V UNITED STATES PATENT OFFICE PROCESS FOR C'ONCENTRATING RUBBER LATEX AND SIMILAR VEGETABLE JUICES Ernst Benzing and. Johannes Jaenicke, Frankfort-on-the-Main, Germany, assignors, by mesne assignments, to Revertex Limited, Londn,'England, a corporation of England No Drawing. Application November 29, 1935, Serial No. 52,193. In Germany December 5, 1934 9 Claims. (01. 18-50) This invention relates to a process for concenresulting from the first step concentrated ditrating rubber latex and similar vegetable juices, rectly. It is also possibleto revert the order of the. and to the product of such process. first two steps.

Heretofore attempts to produce rubber latex The desensitized latex is admirably adapted for concentrates were made with pure rubber latex the production of concentrates by evaporation .5"

or with latex such as contained antiputrefactive because, in consequence of its exceedingly small agents. In this manner, but a slightly increased content of substances that are sensitive to heat, concentration could be obtained because coagulait can be inspissated to form surprisingly stable tion very soon set in during the operation due concentrates, without skinning and coagulation,

10 to the fact that natural rubber latex contains even without the addition of protective colloids. 1o

non-rubber substances which counteract its pow- The latex derived from latex which has been ers of resistance to coagulating influences. pre-treated in accordance with the present in- The object of the present invention is to treat Vention can be employed with advantage for the the latex first by partially coagulating it and production of latex concentrates by centrifuging.

l5 removing the coagulated matter thereby desensi- In such case not only is the high degree of purity tizing the latex by eliminating those substances of the resulting cream of importance, but also which render it susceptible toward coagulating the fact that the efiiciency of the centrifuge is influences and second by concentrating the deincreased because, owing to the greater mechansensitized latex previous to which concentrating, ical stability of theldesensitized latex, the troublethe desensitized latex may, if desired, be treated some cleaning of the centrifuge, hitherto neces- 20 with adsorptive media by which treatment the sary after short working periods has to be uncontent of sensitizing substances in the latex is dertaken only at comparatively rare intervals. still further reduced. Moreover, in the case of desensitized latex, the

The present invention accordingly comprises centrifuging can be easily performed at elevated first removing a portion of the sensitizing subtemperature, which hitherto has been a matter 25 stances from the rubber latex and then concenof considerable difiiculty owing to the known trating the latter'in known manner and in an sensitiveness of latex to the influence of temalkaline or acid condition, for example by evapperature. oration, creaming, centrifuging, filtering, or by Creaming also is facilitated by the desensitizing several of these methods in combination. Parpretreatment of the latex in accordance with the 30 ticularly good results are obtained when the stapresent invention. The separation of serum is bility of the rubber latex is improved by adding accelerated to a greater degree than in the case stabilizing agents, such as protective colloids, in of untreated latex, and a cream characterized by addition to removing the sensitizing substances. a high rubber content and particularly low con- The stabilizing agents may be added before, durtent of non-rubber constituents is obtained, to-"- 3;;

ing, or after concentration. gether with a remarkably clear serum.

The non-rubber constituents which lower the In respect of filtration properties, the pretreatstability of the latex may be removed, in accordment of the present invention also has an exance with this invention as follows. First, the; tremely favorable effect'on the latex. Compara- 40 alkaline or acid latex, treated with protective coltively coarse deposits are obtained on the filter, 4c

loids and/or preservatives if desired, is partially and the pores of the latter become clogged'far coagulated and the coagulum separated, prefer less rapidly than in the case of ordinary latex. ably by a sieve. In such case, the coagulants may In the case of the latex concentrates produced consist for example, of electrolytes and/or nonin accordance with the present invention, the risk 15 electrolytes, such as alcohol or colloidal ferric of decomposition by bacteria islessened to an oxide in a state of true or colloidal solution. e tr o d y de reasince the c ncentrates con- Second, the remaining latex is treated with actain only fractional amounts of the decompostive charcoal, silica gel, aluminum oxide or ferric able substances normally present (proteids and oxide by which any soluble non-rubber substances carbohydrates in particular). This advantage of which counteract the powers of resistance to cothe present process finds expression in a sensible agulating influence are adsorbed. Third, the latex economy of preservatives. thus desensitized is concentrated in any of the Hitherto, it has been impossible in practice to various methods mentioned above. If desired produce concentrates with such a high degree of the second step, that of treating the latex with purity asis obtainable by the process of the presadsorbing media, may be omitted and the latex ent-invention. It has already been proposed, it Y removing a portion of the serum, b-y'centrifuging,

' articles.

filtration or'c reaming, andto repeat these operaliens-after the addition iof clean water in each case-until theseparated sera: contain the bulk 1 of the non-rubber constituents. This procedure, however, is so expensive and complicated that it is suitable only for laboratory work, but not for.

the production of concentrates onamanufacturingscalerv The latex concentrates produced by the process of the present invention form -a valuable new starting material for the inudustries employing Q therefrom .as by a sieve, and treating the remainrubber latex; and, since they furnish colorless, quick-drying and non tacky films, areadmirably adapted 'for the production of dipped and spread served by adding a little sodiumbisulphite in. the

1. A process for producing a relatively stable concentrated rubber latex which comprises the steps of desensitizing the latex by partially coagulating the latex, separating the coagulum therefrom as by a sieve, and Vtreating the remaining latex with media to 'adsorb the non-rubber substances which tend to render the'lat'ex sensisaid desensitized latex;

concentrated. rubber latex which comprises the steps of desensitizing the latex by 'partiallycoagulating the latex; separating the coagulum ing latex with media to adsorb the'non-rubber. substances which te'nd to render the latex sensitiveto coagulating influences and concentrating said desensitized. latex by evaporation;

3. A process for" producing a relatively stable concentrated rubber latex which comprises the steps of desensitizing; the-latex, by" partially 'cotive to coagulating influences and concentrating tapping cups, 100l) kgs.' weretreated by gradually adding '36 litres of formic acid (0.8% strengthh After gently stirring for 3 hours, a coarse, yellow agulating the latex; separating: 'thefcoagulumi; 7 therefrom as by a sieve; and treating the remain? ing latex 'with media to adsorbjthe non-rubber coagulum'had formedpln order tobhechthe,

progressof the coagulation, ammonia" was; added g V until titrationfof} the latex with methyl red'as'in- 'dicato'r disclosed'analkalinityof-ZSO'milli-equiva 40: -afterthe additionof 250imil1i-equivalents of NH! lents per litre. The] coagulum' was then-'sepa rated'by means of anickelsieve. The latex prey treatediby partial coagulation in this manner was contzentrated, by, evaporation} to' a content; of 78.7% of dry substance and "containing. only 0.4% of coagulated matter. Dry filmsproduced the concentrate had merelyfa slightly yel low tinge and low hygroscopic properties 'x mp 1,

Rubber latex'pretreated by partial coa u ation: with formic acid, as was-concentrated in thecentrifuge, 'at 65' C.

per litre. The "resulting cream contained 6'1.8% of dry substance andless than 0.1 of coagulatedmatter. I No non-reversible substances were pre cipitated Jon dilution of the cream with water.

Rubber precipitated from thecream had a protein content of 0.9% and 1 a content of -1'.4%' of substances soluble in acetone. I V j V 7 Example 111' H Rubberslatex pretreated by partialcoagulationi; with formic acid and subsequently renderedal-i kaline as in Example 1, Waspallowed topass; a layer of active charcoal which had been steamed; and slightly dried. The latex was then ;concen-.

trated by evaporation in a concentrator described 7 in the copending application Serial No. 509,660. The concentrate contained, ,715.6%, of dry sub: stance; The content of non-coagulable'dissolved} o1'; dispersed constituents inthe concentrate'; Ibasedon the crepe content, was'only 2.9 The 1 amount of irreversible matter'presentin'the concentrate was as low-as 0.2.per mille, We claim: I

substances whichtend to renderthe latexysehing said desensitized latex by centrifuging. :1 14. A process for producing a stable"concen- 'sitiveto coagulatingtinfluencesand ;concentrat-,

trated rubber latex. which comprises thewsteps; v

of desensitizing the latex bypartially coagulating the latex and separating the coagulum therefrom as by'a sieve,- and concentrating the desensitized:-

latex; a

5. Aprocess'for producing a stable concentrat ed rubberlatex which comprises the steps of de,-

sensitizing the latex .by partially'coagulating the 6. A processior producinga stable iconcenl ratg ed rubber latexywhich-comprises the stepsjofi desensitizingthe latex by partially coagulating the latex and separating the coagulumifiere-y from asby a-sieve, and concentrating thedesen- V sitized latex by centrifuging.

'LA, process for producing; a 'stab1 rieA-f trated rubber latex'which comprises the'stepsofj the desensitized latex andseparating; the coagulum therefrom ajs by a sieve, andconcentrating desensitizing' the latex by partially coagulating the latex and separating-the coagulum therefrom;

as by a sieve, and concentrating'the desensitized, latex by creamingp i I 8; A process for-producinga'stable'rubber' latex which comprises-the steps of- "desensitizing the? 7 latex by partially coagulating it byan'organic; acid; separating the coa gulum from the latex as; r s by a, sieve, and concentrating the-desensitized 9. ,A processfor producing-stable rubbery which comprisesthesteps of desensitizing the I 

